Question

在windows下，是不是不能使用python的multiprocessing块呀，就像不能使用os.fork()一样，例子如下：

import os, time,sys,sys
from multiprocessing import *
def test(x):
print current_process().pid, x
time.sleep(1)

p = Process(target = test, args = [100])
p.start()
p.join()

Answer 1

看文档：
python-2.7-docs-html/library/multiprocessing.html#multiprocessing-programming

简而言之，需要在p=Process()前加上
if __name__ == ‘__main__’:
p = Process(...

Safe importing of main module

Make sure that the main module can be safely imported by a new Python interpreter without causing unintended side effects (such a starting a new process).

For example, under Windows running the following module would fail with a RuntimeError:

from multiprocessing import Process

def foo():
print 'hello'

p = Process(target=foo)
p.start()

Instead one should protect the “entry point” of the program by using if __name__ == '__main__': as follows:

from multiprocessing import Process, freeze_support

def foo():
print 'hello'

if __name__ == '__main__':
freeze_support()
p = Process(target=foo)
p.start()

(The freeze_support() line can be omitted if the program will be run normally instead of frozen.)

This allows the newly spawned Python interpreter to safely import the module and then run the module’s foo() function.